"It's a terrible tragedy, it's the sort of thing that probably should never have happened," said Paul Oleksa, a pipeline safety consultant.

Oleksa explains that most pipeline explosions occur when construction crews accidentally cut into a line. That is what happened in Walnut Creek in 2004, when five construction workers lost their lives.

However, there is another incident in which federal investigators concluded that PG&E was too slow responding to a natural gas leak and the California PUC found the utility did not "qualify field service representatives on the use of gas detection equipment."

That incident was Christmas Eve 2008 in Rancho Cordova and the blast destroyed a home, killed one person and injured five others. That happened in a small distribution pipe. The large transmission lines have a better record.

"These pipelines are exceedingly safe," said Oleksa.

Oleksa explains there is new technology to catch weaknesses or leaks in the transmission pipes. These "smart pigs" or pipeline inspection gauges may be up to 15 feet long.

"A pipeline has to built, designed and constructed in such a way that such a contraption, such a large thing, can pass through it," said Oleksa.

The San Bruno pipeline appears to have been built before the smart pig technology. So, chances are it wasn't used in San Bruno, but that is one of the questions to be answered. Along with the main one -- with reports from neighbors who smelled gas, did PG&E fail to act quickly enough?

"Somebody must not have gone down there with a leak detector and what you call, chased it down," said Murphy.

Clearly, that is a major focus of the investigation -- is it true that people there in San Bruno complained about the leak and did PG&E respond?

If you have any information on this topic or any tips that we should check out about the San Bruno blast, contact us at: 1-888-40-I-Team.